1. Field of the Invention
One embodiment generally relates to test of memory devices. In particular, one embodiment relates to systems and methods of repairing memory devices.
2. Description of the Related Art
Semiconductor memory devices can be found in a wide variety of electronics devices. Modern memory devices are relatively large in size and relatively inexpensive. A memory device typically includes at least one array of memory cells arranged in rows and columns. In a relatively large array, it can be expected that some cells will not be usable. Accordingly, redundant rows and columns exist to repair the defective cells via redundancy analysis. Tests are performed on memory devices to identify the cells that need to be replaced. For relatively large arrays, these tests comprising test patterns can be time-consuming and relatively expensive. For example, many test patterns may be run to test for gross failures, and to test for margin such as voltage, speed, and the like.
FIG. 1 is a flowchart illustrating an example of a conventional test and redundancy analysis. For example, the process can be performed by Automated Test Equipment (ATE).
To be more specific, the process starts in step S910. In step S920, a first test pattern is chosen and applied to the device under test (DUT). The test results from step S920, i.e., the information on the failed memory locations (the fails), are collected into a fail capture memory, which is a storage device to store the information on the fails. The fail information from test patterns includes information on the fails such as internal addresses. The solution or solution information from redundancy analysis includes information on which redundant rows or columns would be activated to replace and repair the fails. In step S930, the test results are copied for a redundancy analyzer so that a test pattern and a redundancy analysis for an immediately prior test pattern can be run in parallel. In step S940, Threads 1 and 2 are spawned, and run in parallel, in which the redundancy analyzer starts to process the test results obtained in the step S920 or S960 and stored in the fail capture memory. While the redundancy analyzer processes the fails in step S950, testing with a next test pattern is performed on the DUT in S960 along Thread 1. In the step S950, the redundancy analysis for both the must fail and sparse fails is performed. The redundancy analysis of S950 can take more time or less time to complete than the test pattern S960. When the step S970 waits for completion of the step S950, the test as a whole runs slower than the speed at which the ATE can perform the test patterns, which adds time and cost to the DUT. For example, in the prior art, a second test with “next pattern” S960 is on hold waiting S970 for the redundancy analysis S950 obtained from the first test with “1st pattern” S920 is done. Once the step S950 is done, then the process can return to S930 via S970 to run further test patterns and redundancy analysis, or finishes the process.